It is well appreciated in the art that the interior of a sealed protective suit, such as a sealed space suit, must be cooled so as to prevent excessive heat buildup and maintain a comfortable temperature within the suit for the benefit of the occupant. Without adequate cooling of the interior, the environment within the suit would become unsuitable as heat generated within the suit, largely due to the occupant's metabolism, and heat energy transferred from the external environment build up.
Accordingly, it is customary for the occupant of such a protective suit to wear under the suit a garment which is liquid cooled to remove metabolic heat rather than allowing it to build up within the interior of the suit. Typically, the liquid cooled garment (LCG) includes a plurality of flexible tubes forming a cooling network about the occupant's body through which a suitable coolant, generally water, is pumped as a heat sink fluid. Such liquid cooled garments are disclosed for example in U.S. Pat. Nos. 3,289,748, 3,295,594 and 3,400,756. As the coolant traverses the tubular network, the coolant absorbs heat thereby increasing its temperature. After completing its traverse of the network of cooling tubes in the LCG, the coolant is collected for recycle. Before the coolant is suitable for recycle, the heat picked up in traversing the tubular network of the LCG must be removed.
One technique for removing this heat involves passing the coolant in heat exchange relationship with a heat sink containing a phase change material which will absorb heat from the coolant and in the process will undergo an endothermic phase change. Thus, not merely the heat capacity of the material, but more importantly the heat of fusion of the material provide the heat sink. At least a portion of the heat absorbed by the heat sink is transferred therefrom to the surrounding exterior environment. After a period of time, the heat sink must be regenerated by cooling the phase change material to reverse its phase change thereby bringing the material back to its original state and preferably to also subcool the material.
An apparatus adapted to cool a coolant for a protective suit by this technique, and particularly suited to be worn as a backpack by an occupant of a sealed space suit during extravehicular activity, is presented in commonly assigned, co-pending application Ser. No. 593,599 filed Oct. 4, 1990, as a continuation of application Ser. No. 325,426, filed Mar. 20, 1989. The apparatus disclosed therein for cooling the coolant from a liquid cooled garment comprises a radiator-based, non-venting cooling system utilizing a single phase change material stored in a plurality of panels which form the exterior of the backpack worn during extravehicular activity. Each panel is formed of layered components comprising, from the interior (i.e. nearest the occupant) to the exterior (i.e. exposed to the environment): a layer of coolant circulation tubes disposed against the interior facing surface of a heat distribution plate, a plurality of thermoelectric heat pump modules distributed over the exterior facing surface of the heat distribution plate, a heat storage panel disposed on the array of heat pump modules and containing the phase change material, and a coating on the exterior surface of the heat storage panel for enhancing radiation of heat therefrom to a vacuum environment. The phase change material is defined as being any material which changes phase from about 40.degree. F. to 65.degree. F., with a paraffin based substance or mixture, preferably n-hexadecane paraffin, being the desired phase change material since it has a phase change temperature which lies near the average between the highest and lowest LCG coolant temperatures typically required during extravehicular activity in space. Although well suited for use as a portable cooling system, the attractiveness of such an apparatus would be enhanced if the volume occupied by the layered components could be reduced and if the number of thermoelectric heat pump modules required could be reduced thereby simplifying the complex wiring network associated therewith and reducing electric current and power usage.
Accordingly, it is an object of the present invention to provide a lower volume, lower power consuming, non-venting cooling apparatus for transferring heat from a liquid cooled garment coolant to a surrounding environment.
It is a further object of the present invention to provide a regenerable, non-venting cooling apparatus utilizing two different phase change materials as heat sinks for transferring heat from a liquid cooled garment coolant of a space suit to a surrounding vacuum environment during extravehicular activity.